LOANS (Schedule of Loans Outstanding, by Classification) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Total loans	$ 3,798,590	$ 3,704,440
Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	100.00%	100.00%
Unallocated Financing Receivables [Member]
Total loans	$ 432	$ 402
Unallocated Financing Receivables [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	0.01%	0.01%
Residential Mortgage [Member] | Residential Portfolio Segment [Member]
Total loans	$ 562,620	$ 576,356
Residential Mortgage [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	14.81%	15.56%
Multifamily Property [Member] | Residential Portfolio Segment [Member]
Total loans	$ 1,285,816	$ 1,388,958
Multifamily Property [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	33.85%	37.49%
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans	$ 644,900	$ 626,656
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	16.98%	16.92%
Commercial Loans Including Equipment Financing [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans	$ 1,180,414	$ 958,294
Commercial Loans Including Equipment Financing [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	31.08%	25.87%
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member]
Total loans	$ 59,930	$ 67,497
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	1.58%	1.82%
Consumer Loans, Including Home Equity Loans [Member] | Consumer and Other Loans [Member]
Total loans	$ 64,478	$ 86,277
Consumer Loans, Including Home Equity Loans [Member] | Consumer and Other Loans [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	1.69%	2.33%